The current application seeks to investigate the role of chronic daily stress in the course of postpartum depression, the negative impact on infant cognitive and emotional development, and the mediating role of the mother-infant relationship on infant development. Chronic stress is linked to the onset and course of depression, and as many as 19% of women (49% of Mexican-American women) suffer from postpartum depression, making it a significant public health concern. Exposure to maternal depression during early infancy has significant long-term effects on several developmental processes. There is a substantial literature that details the negative effects of postpartum depression on infant adaptation, including deficits in both cognitive functioning and the development of emotion regulation skills. It is possible that these developmental competencies may be dependent upon mother-infant relationship quality, and that this relationship mediates the effects of maternal depression. The proposed research plan will test several models to address the role of daily stress, the impact of depression on the mother-infant relationship and infant competencies, and the mediational role of the quality of the mother-infant relationship on infant development. Data will be drawn from a larger longitudinal study that explores coregulatory processes between infants and their depressed, Mexican-American mothers. Measurements include maternal self-reports of stress, depression, and infant emotional regulation; observations of mother-infant interactions; and assessment of infant cognitive and emotional development across the first postpartum year. These data allow the opportunity to longitudinally explore important public health issues related to postpartum depression and infant development in a high risk population.